Reciprocating pump for liquefied gases



P 1948- c. R. ANDERSON 2,440,216

RECIPROCATING PUIP FOR LIQUEFIED GASES Filed June 4, 1945 2 Sheets-Sheet1 l\\\ \g. CARL R. ANDERSON Patented Apr. 20,

2,440,216 1 RECIPROCATING PUMP FOR LIQUEFIED GASES Carl R. Anderson,Chattanooga, Tenn",

to Air Products, Incorporated, Chattanooga, Tenn., a corporation ofMichigan Application June 4, 1945,,Serlal No. 597,486

7 Claims. 1

This invention relates to a structural improvement in the cold orpumping end of a reciprocating pump designed to handle liquefied gasesat very low temperatures.

The purpose of the invention is to provide.

means for avoiding gas-lock due to vaporization of the liquefied gas byatmospheric or frictional heat transmitted to the liquid through thecylinder wall and the plunger.

The invention may best be understood with reference to the attacheddrawings and the following description thereof, in which Fig. 1 is alongitudinal section through the cold or pumping end of a reciprocatingpump adapted to the handling of liquefied gases, as for example liquid.oxygen;

Fig. 2 is an end view of the same, as on the line 2-2 of Fig. 1; i

Fig. 3 is an enlarged view, partly in section,

and partly in elevation, of the spacing element generally indicated at20 in Fig. 1: i

Fig. 4 is a section through the spacing element, as on the line |4 ofFig. 3;

Fig. 5 is a longitudinal view, partly in section and partly inelevation. of a modified form of the spacing element 20;

Fig. 6 is a cross section through the same, as on the line 6-6 of Fig.5;

Fig. 7 is a longitudinal section through another modified form of thespacing element 20.;

Fig. 8 is an end view of the same, as on the line 8-8 of Fig. 7;

Fig.9 is a longitudinal section through the cold end of a modified formof pump, in which the spacing element 20 is dispensed with and the pumpbody is hollowed out to provide space for the liquid which cools theplunger;

Fig. 10 is a sectional view of a fragment of the structure of Fig. 9modified by the insertion of a guide bushing, and

Fig. 11 is a cross section as on the line ll-l I of Fig. 10.

Referring first to Fig. 1, a metallic cylinder l0 is inserted into ahead block ll into which are connected an intake valve l2 and adischarge valve I 3 for the liquid to be pumped. The cylinder issurrounded by a gas jacket M. a cold gas such as the vapor of boilingliquid nitrogen entering at l5, passing through ports lG-IB (see.

Fig. 2) and being discharged at II. This nitrogen vapor. which will bein the saturated condition if protected from heat infiltration up to thepoint 'of use, may be drawn from the nitrogen outlet of an airfractionating column if the pump be used in that connection, or may beproduced by evaporating liquid nitrogen in any closed refrigeratingcycle.

Within the cylinder is a plunger l8 which is reciprocated longitudinallyby means not shown. Surrounding the plunger and adjacent its working endis a working barrel I! of metal, bearing at one end against the headblock and tightly fitted within the end of the cylinder. This bar- .relshould be bored to give a slight radial clearance over the rod, as ofthe order of 0.05" to 0.10".

Bearing against the end of the working barrel is a spacing element 20,shown in more detail in Figs. 3 and 4 and in slightly modified forms inFigs. 5 and 7. This element, in the form shown in Fig. 3, consists of asleeve 20' interposed between two guide bushings 2l' and 2|". The tubeshould be. closely but slidably fitted within the cylinder and the guidebushings are bored to a neat running fit on the plunger and are providedeach with one or more perforations 22.

The-material of theseguide bushings should be a metal having a lowcoefiicient of friction with the metal of the plunger together withsufflcient toughness to avoid excessive wear. Leaded bronze isrecommended for this purpose, but other metals having the requiredproperties may be substituted.

Bearing against the spacing element is a packing assembly 23, hereillustrated as a soft pack- .nut serves to hold it in place, or analternative bolted arrangement may be substituted for the nut.

The crank, cross-head and other actuating members, not shown, areconnected with the cylinder through a rigid disc or block 26 and ametallic frame 2'! of which only a fragment appears in the drawing.

In the operation of the above described structure in the pumping ofliquids which boil at extremely low temperatures, as for example liquidoxygen, the constant leakage of at least small' quantities of heat intothe liquid-containing end of the pump is unavoidable. Atmospheric heatis excluded from the wall of the'cylinder by the. flow of cold gaspassing through jacket I4 and this gas fiow, as will be described,abstracts heat from the liquid within the cylinder. But some atmosphericheat is transmitted through the length of the plunger, the outer end ofwhich must of necessity be warmer than the displacing end, and avariable but usually greater quantity of in avoiding gas-lock. By reasonof the perforai tions 22" in the left or outer guide bushing 2|", 1

the liquid oxygen or other liquefied gas being pumped has access to thespace 28 surrounding the rod and within tube 20', and in actualoperation this pocket is constantly filled with the liquid. The entirelength of, plunger projecting beyond the inner face of guide bushing 2f?(the bushing adjacent packing element 23) is bathed in the pumpedliquid, either continuously or, as regards short portion of the plunger,as these portions emerge from the packing or bushings. The heat whichwould otherwise fiow to the tip of the plunger is abstracted by thesurrounding liquid and that portion of the plunger located within theworking barrel is maintained at a temperature below the boiling point ofthe liquid being pumped.

The heat withdrawnfrom the plunger by the liquid in pocket 29 is in turnimparted to tube 20' and, as this tube is in heat conductive contactwith the wall ofcylinder l0, the heat is finally transmitted to the gasflowing through the jacket and is thereby withdrawn from the system.

The refrigerative effect of the cooling gas is thus exercised throughthe cylinder and tube walls in maintaining the liquid in pocket 29, andthe projecting portion of the plunger, at temperatures below the boilingpoint of the pumped liquid. In the instance of pumping liquid oxygen,the difference of approximately 12.8 C. between the boiling point ofthis liquid and the temperature of saturated nitrogen vapor is ample toprovide the rate of heat flow necessary to produce this result.

The liquid in pocket 29 is subjected to a periodic elevation anddepression of temperature during the pumping cycle. The pocket shouldtherefore be of such size that its liquid contents will have sufiicientheat absorbing capacity to prevent flashing under the most adverseconditions of temperature and pressure encountered during the. cycle.

In order to limit the extent to which the surface of the plunger isenclosed in metal and thus deprived of liquid contact, it is desirableto make the guide bushings 2l'-2i" as short as is consistent withreasonable durability. Their combined length should not exceed andpreferably should be less than the maximum stroke of the pump plunger.The bushings should be spaced as far apart as structural conditions willpermit, to provide the maximum area of contact between metal and liquid.

It will be noted that the perforations'22' in bushing 2|, adjacent thepacking assembly, are nonfunctional. These perforations may beomitdesired to increase transfer eflectiveness to the limit, one of themodified forms of spacer illustrated in Figs. 5 and '1 may be used. Inthe form of Fig. 5 the guide bushings are as above described but thespacing tube 20 of the first form is replaced by three or more studs 30,forming an open cage. In the form of Fig. 7 a tube 8| is used to spacethe bushings, this tube being of diameter greater than that of theplunger and less than that of the interioriof the cylinder, so as to.occupy a medial position. In this form the spacing tube is provided witha number of perforations 32 for the circulation of liquid. In

the use of these equivalent forms the liquid in space 29 is in directcontact with the wall of the cylinder and heat transfer from metal tometal is avoided.

ted, but it is desirable to make the spacer assembly symmetrical inorder to avoid the blinding of pocket 29 by the inadvertent insertion ofthe spacer in reversed position.

The metal. to metal contact between tube 20' V and cylinder wall Illinterposes some slight resistance to the flow of heat from the liquid inthe pocket to the gas in the jacket and, if it is In none of the abovealternatives is it necessary that the two bushings be identical, northat they be rigidly interconnected. It is essential, of course, thatthey be spaced longitudinally to permit the maintenance of a body of thepumped liquid between them.

The maintenance of a cooled body of the pumped liquid surrounding theplunger, which is the essential step of this invention, may be attainedwithout the use of a separable spacing element, in the mannerillustrated in Fig. 9. In this construction a body block 33 is bored forpart of its length to form the working barrel 34, the remainder of thelength being bored to a larger diameter to leave a liberal annular spacebetween the plunger and the wall "I which corresponds with the cylinderwall of the previous forms. The insertion of 'a packing box 25 into theopen end of the larger bore converts this annular space into a pocket 29which communicates with the working barrel and functions as previouslydescribed. The gas jacket I is positioned over the body block and issupplied with cooling gas in the manner illustrated in Fig. 1.

The structure illustrated in Fig. 9 does not provide any guide for theplunger at its point of en-' try into the working barrel. If the plungerbe of such small diameter as to be subject to distortion when pumping athigh heads, a guide may be provided in the manner illustrated in Figs.10 and 11. In this modification of the form of Fig. 9, a bushing 36closely fitting the plunger is pressed into the bottom of pocket 29,channels 31 being grooved in the face and periphery of the bushingbefore it is inserted, to provide for the passage of liquid into and outof the pocket.

The instant application is a continuationin-part of my copendingapplications Serial No. 507,091, filed October 21, 1943, and Serial No.548,846, filed August 10, 1944.

I claim as my invention:

1. In a-pump for liquefied gases: a plunger of uniform diameterreciprocating in a working barrel; a cylinder surrounding and spacedfrom said plunger; packing between said plunger and said cylinder, anda, spacing element separating said packing from the end of said workingbarrel, said element comprising a pair of guide bushings arranged tomaintain said plunger concentric with said cylinder and means formaintaining said bushings in spaced relation, at least one of saidbushings being perforated at a point spaced from'said plunger to allowthe pumped liquid to fiow from said working barrel into the spacebetween said bushings.

2. In combination with a reciprocating plunger pump having a cylinderand a working barrel and plunger packing within said cylinder, a spacingelement adapted to be placed between said packing and said workingbarrel, said element comprising: a pair of guide bushings arranged tomaintain said plunger concentric with said cylinder and means forretaining said bushings in spaced relation, the bushing adjacent saidworking barrel having a perforation additional to the bore through whichsaid plunger passes.

3. A spacing element substantially as and for the purpose set forth inclaim 2, in which saidretaining means consists of a metallic tubeconfrom said plunger, said means comprising: a

jacket surrounding said cylinder and means for continuously passing arelatively cold fluid through said jacket to cool the wall of saidcylin-' der; a guide bushing arranged to maintain said plungerconcentric with the bore of said working barrel, said bushing beingperforated at a point spaced from said plunger, and means for widelyspacing said bushing from said packing element to provide a chamber forthe reception oi pumped liquid flowing from said working barrel throughsaid perforated bushing. said liquid cooling-said plunger intransmitting heat therefrom to the cooled wall of said cylinder.

6. A pump for liquefied gases comprising a pumping chamber provided withintake and discharge valves; a reciprocating plunger, and a body blockhaving a bore in which said plunger 40 1,879,370

reciprocates. the portion of said bore directed away Iromsaid pumpingchamber being enlarged to provide an annular space surrounding saidplunger; an element including plunger packing closing the end of saidannular space to form a liquid-retaining chamber, said retaining chamberbeing in communication with said pumping chamber; a jacket surroundingsaid body block, and means for passing through said. jacket a stream offluid at a temperature sufficiently low to withdraw heat from said bodyblock and from the liquid in said retaining chamber.

.7. A pump for liquefied gases comprising a pumping chamber-providedwith intake and discharge valves; a reciprocating plunger. and a bodyblock having a bore in which said plunger reciprocates, the portion ofsaid bore distant from said pumping space being enlarged to form a wideannular space surrounding said plunger and the portion of said boreadjacent-said pumping space being of a diameterslightly greater thanthat of said plunger to provide a working barrel; a guide bushingclosely fitting around said plunger in the -end of said annular spaceadjacent said working Number barrel; means permitting the flow of pumpedliquid around said bushing and between said barrel and said annularspace; a closure for the end of said annular space opposite saidbushing; a jacket surrounding said body block, and means for passingthrough said jacket astream of fluid at a temperaturebelow theatmospheric pressure boiling point of the liquefied gas being pumped.

- CARL R; ANDERSON.

REFERENCES CITED The following references are of record in the flleofthis patent:

UNITED STATES PATENTS Name Date 144,390 Day Nov. 11, 1873 McAilisterSept. 27, 1932 2,292,617 Dana Aug; 11, 1942 2,330,781

Langmyhr et al. a Sept. 28, 1943

